Conventionally, non-contact voltage measuring devices have been disclosed which measure a voltage (measurement target voltage) that causes an alternating current to flow through a conducting wire contained in a wire subjected to insulating coating, without being in contact with the conducting wire.
Generally, a non-contact voltage measuring device includes a probe and an electric circuit. In a case where the probe is brought closer to a wire so that a coupling capacitance is formed between the probe and the wire, a measurement target voltage is derived in accordance with a voltage signal supplied to the electric circuit via the probe. An electric field shield for shielding the electric circuit from an external electric field is provided around the electric circuit.
Generally, as the probe becomes closer to the wire, a capacitance value of the coupling capacitance becomes higher. This causes an improvement in accuracy of measurement of the measurement target voltage. Therefore, the probe is preferably provided as close as possible to a surface of the wire. Furthermore, the non-contact voltage measuring device is preferably capable of measuring measurement target voltages applied to various wires having respective different diameters.
However, according to such a conventional non-contact voltage measuring device, it is sometimes not possible to bring the probe sufficiently closer to the wire, depending on a diameter of the wire. In this case, the capacitance value of the coupling capacitance becomes lower, and accordingly the accuracy of the measurement of the measurement target voltage becomes lower.